Polymerization of ethylene and ethylene/1-hexene over Ziegler–Natta/metallocene hybrid catalysts supported on MgCl2 prepared by a recrystallization method

MgCl₂ for use as a catalyst support was prepared by dissolution in methanol and recrystallization in n-decane, followed by vacuum-drying at 2,000 rpm. The prepared support was modified by treatment with alkylaluminum compounds. The activity profile of ethylene over the supported catalysts persisted for periods up to 1 h during the polymerization. The prepared Ziegler–Natta/metallocene hybrid catalysts exhibited the characteristics of both metallocene and Ziegler–Natta catalysts. The polymer produced by the hybrid catalysts gave bimodal peaks in differential scanning calorimetry analysis for ethylene and ethylene/1-hexene polymerization, suggesting that the polymer was composed of two different lamellar structures that were polymerized by each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1707–1715, 1998     

Different behaviors of metallocene and Ziegler–Natta catalysts in ethylene/1,5‐hexadiene copolymerization

The behaviors of three different catalyst systems, TiCl₄/MgCl₂, Cp₂ZrCl₂ and Cp₂HfCl₂, were investigated in ethylene/1,5‐hexadiene copolymerization. In the Fourier transform infrared spectra of the copolymers, cyclization and branching were detected for 1,5‐hexadiene insertion in the metallocene and Ziegler–Natta systems, respectively. DSC and viscometry analyses results revealed that copolymers with lower T_m and crystallinity and higher molecular weight were obtained with metallocene catalysts. The sequence length distribution of the copolymers was investigated by using the successive self‐nucleation and annealing thermal fractionation technique. The continuous melting endotherms obtained from successive self‐nucleation and annealing analysis were employed to get information about short‐chain branching, the branching dispersity index, comonomer content and lamella thickness in the synthesized copolymers. The results established that metallocene catalysts were much more effective than Ziegler–Natta catalysts in the incorporation of 1,5‐hexadiene in the polyethylene structure. Metallocene‐based copolymers had higher short‐chain branching and comonomer content, narrower branching dispersity index and thinner lamellae. Finally, the tendency of the employed catalysts in the 1,5‐hexadiene incorporation and cyclization reaction was explored via molecular simulation. The energy results demonstrated that, in comparison to Ziegler–Natta, metallocene catalysts have a much higher tendency to 1,5‐hexadiene incorporation and cyclization. © 2018 Society of Chemical Industry     

Stereospecific polymerization of olefins with supported Ziegler − Natta catalysts

The discovery of Ziegler ? Natta catalysts has been one of the greatest developments in technology for the synthesis of stereoregular polymers in both academy and industry since the 1950s. In particular, the development of the fourth generation Ziegler ? Natta catalyst with MgCl₂ as support brings a revolutionary improvement to the properties of manufactured polyolefins and stimulates people to explore the stereospecific polymerization of α‐olefin and diene monomers, which supplies the power to synthesize a new type of polyolefin materials. Although research on single‐site catalysts has attracted a lot of attention in recent years, the ‘old’ and conventional Ziegler ? Natta catalysts are still being developed vigorously due to their unique industrial advantages such as low cost, high catalytic efficiency and high stereospecificity. In this mini‐review, we mainly summarize the development of the conventional supported Ziegler ? Natta catalyst system and the stereoregular polyolefins synthesized with supported Ziegler ? Natta catalysts. © 2013 Society of Chemical Industry     

Characteristics of ethylene polymerization over Ziegler–Natta/metallocene catalysts Comparison between hybrid and mixed catalysts

Two types of inorganic supports, MgCl₂ and SiO₂, for the impregnation of catalysts were prepared by the recrystallization and the sol–gel method, respectively. The polyethylene produced by the Ziegler–Natta/metallocene hybrid and mixed catalysts showed two melting temperatures and a bimodal MWD corresponding to products arising from each of the individual catalysts. This suggests that these Ziegler–Natta/metallocene catalysts acted as individual active species, and as a result, produced a blend of polymers.     

Hybrid titanium catalyst supported on core‐shell silica/poly(styrene‐co‐acrylic acid) carrier

Hybrid titanium catalysts supported on silica/poly(styrene‐co‐acrylic acid) (SiO₂/PSA) core‐shell carrier were prepared and studied. The resulting catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, laser scattering particle analyzer and scanning electronic microscope (SEM). The hybrid catalyst (TiCl₃/MgCl₂/THF/SiO₂·TiCl₄/MgCl₂/PSA) showed core‐shell structure and the thickness of the PSA layer in the two different hybrid catalysts was 2.0 μm and 5.0 μm, respectively. The activities of the hybrid catalysts were comparable to the conventional titanium‐based Ziegler‐Natta catalyst (TiCl₃/MgCl₂/THF/SiO₂). The hybrid catalysts showed lower initial polymerization rate and longer polymerization life time compared with TiCl₃/MgCl₂/THF/SiO₂. The activities of the hybrid catalysts were enhanced firstly and then decreased with increasing P/P. Higher molecular weight and broader molecular weight distribution (MWD) of polyethylene produced by the core‐shell hybrid catalysts were obtained. Particularly, the hybrid catalyst with a PSA layer of 5.0 μm obtained the longest polymerization life time with the highest activity (2071 kg PE mol^?1 Ti h^?1) and the resulting polyethylene had the broadest MWD (polydispersity index = 11.5) under our experimental conditions. The morphology of the polyethylene particles produced by the hybrid catalysts was spherical, but with irregular subparticles due to the influence of PSA layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Characterization of commercial linear low‐density polyethylene by TREF‐DSC and TREF‐SEC cross‐fractionation

A new technique for characterization of linear low‐density polyethylene (LLDPE) is presented in this report. The molecular structure of two commercial LLDPEs, produced by copolymerization of ethylene with 1‐butene over a Ziegler‐Natta and a metallocene catalyst, was investigated. The LLDPE resins were fractionated by temperature rising elution fractionation (TREF), and the TREF fractions were further analyzed by size exclusion chromatography and differential scanning calorimetry (DSC) coupled with successive nucleation/annealing (SNA). The cross‐fractionation techniques provided detailed information about the molecular structure of different types of LLDPEs; of particular interest is the TREF‐SNA‐DSC cross‐fractionation which allowed a direct observation of methylene sequence distribution and thus short chain branch (SCB) distribution. TREF‐size exclusion chromatography cross‐fractionation showed that the molar mass of the Ziegler‐Natta LLDPE increased monotonically with decreasing SCB, whereas the plot of M_w vs SCB for the metallocene LLDPE showed a maximum. TREF‐SNA‐DSC cross‐fractionation clearly showed that the metallocene LLDPE only had intramolecular heterogeneity in SCB distribution, whereas the Ziegler‐Natta LLDPEs exhibited both intermolecular and intramolecular heterogeneity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 960–967, 2000     

Polymer-supported heterogeneous titanium-based Ziegler-Natta catalyst for ethylene polymerization

Reported here in, is the synthesis of polystyrene (PS)-supported Ziegler–Natta catalyst (PS-TiCl₄) by the reaction of PS and titanium tetrachloride (TiCl₄). PS was synthesized by emulsion polymerization using super critical CO₂ (sc-CO₂) as a medium. Three catalysts were synthesized by varying the TiCl₄/PS weight ratio in hexane medium. The resulting catalysts were characterized by Fourier transformed-infrared spectroscopy, UV–visible spectroscopy, scanning electron microscope and energy dispersive X-ray detector, X-ray diffraction analysis. The acidity of the catalysts in an acetone/water solution was measured by pH meter. The thermogravimetric analysis reveals that catalysts are stable upto 150–180°C. Due to their higher degree of thermal stability these catalysts may potentially be used as a support in conventional Ziegler–Natta catalyst for ethylene polymerization. These catalysts also showed good storability and its overall catalytic productivity are found to be 3720 g PE/g Ti. The productivity of the catalysts also depended on the titanium concentration in the polymer matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ultraviolet‐induced degradation of Ziegler‐Natta and metallocene catalyzed polyethylenes

The metallocene revolution has aroused a storm of interest and associated questions regarding the performance and durability of polyolefins. This new technology has impacted the additives used to stabilize and process polymers. In this work, Ziegler‐Natta and metallocene polyethylene (PE) samples were exposed to natural weather conditions under high doses of ultraviolet radiation, high temperature, and increased humidity. Weather‐induced degradation of the two sets of PEs was studied using gel permeation chromatography, mechanical properties testing, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The gel permeation chromatography analysis indicated the change in molecular weight distribution and molecular weights of metallocene PE to be more stable than conventional Ziegler‐Natta PE. The tensile properties of metallocene PE are known to have higher values than Ziegler‐Natta PE. The former exhibited a lower drop rate in mechanical properties when exposed to natural weather. Formations of nonvolatile carbonyl oxidation products, which absorb in the infrared region with a maximum absorbance level at 1742 cm⁻¹ were determined. This indicated a higher rate of photo‐oxidative and thermal degradation of Ziegler‐Natta PE as compared with metallocene PE. The ultraviolet stabilization of metallocene PE may require different doses and a new kind of stabilizer system that can impart a longer useful lifetime and are cost effective for PE used for outdoor purposes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1591–1596, 2000     

Ethylene polymerization using a novel MgCl2/SiO2‐supported Ziegler–Natta catalyst

A novel MgCl₂/SiO₂‐supported Ziegler–Natta catalyst was prepared using a new one‐pot ball milling method. Using this catalyst, polyethylenes with different molecular weight distributions were synthesized. The effects of the [Si]/[Mg] ratio, polymerization temperature and [Al]/[Ti] ratio on the catalytic activity, the kinetic behaviour and the molecular weight and the polydispersity of the resultant polymer were studied. It was found that the polydispersity index of the polymer could be adjusted over a wide range of 5–30 through regulating the [Si]/[Mg] ratio and polymerization temperature, and especially when the [Si]/[Mg] ratio was 1.70, the polydispersity index could reach over 25. This novel bi‐supported Ziegler–Natta catalyst is thus useful for preparing polyethylene with a required molecular weight distribution using current equipment and technological processes. Copyright © 2005 Society of Chemical Industry     

Modeling of the propylene polymerization catalyzed by single‐/multi‐active site catalyst: A Monte Carlo study

In the present study, a model is established to describe the propylene polymerization kinetics catalyzed by the typical catalysts with single‐/multi‐active site type in a liquid phase stirred‐tank reactor using the Monte Carlo simulation method, regardless of the mass and heat diffusion effects within the polymer particles. Many kinetic data, including polypropylene yield, concentration transformation of catalyst active sites, number–average molecular weight, etc., are obtained by the model. The simulated kinetic results are found to be in agreement with the reference ones obtained in a population balance model. Furthermore, the comparisons of the kinetic data between the polymerization catalyzed by the catalyst with single‐active site type (typically silica‐supported metallocene) and the catalyst with multi‐active site type (typically MgCl₂‐supported Ziegler‐Natta catalyst) have been studied using the model. Especially, the effects of hydrogen on the polymerization are studied using the model. The studied results show that the theory of catalyst active site can be used to explain the different propylene polymerization kinetics catalyzed by the typical catalyst with single‐/multi‐active site type. In addition, the role of hydrogen in the propylene polymerization needs to be emphasized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of polypropylene/clay nanocomposites using bisupported Ziegler‐Natta catalyst

In this article, preparation of polypropylene/clay nanocomposites (PPCNC) via in situ polymerization is investigated. MgCl₂/montmorillonite bisupported Ziegler‐Natta catalyst was used to prepare PPCNC samples. Montmorillonite (MMT) was used as an inert support and reinforcement agent. The nanostructure of the composites was characterized by X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. Obtained results showed that silica layers of the MMT in these PPCNC were intercalated, partially exfoliated, and uniformly dispersed in the polypropylene matrix. Thermogravimetric analysis showed good thermal stability for the prepared PPCNC. Differential scanning calorimetric was used to investigate both melting and crystallization temperatures, as well as the crystallinity of the PPCNC samples. Results of permeability analysis showed significant increase in barrier properties of PPCNC films. Effective parameters on molecular weight and flow ability of produced samples such as Al/Ti molar ratio and H₂ concentration were also investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Supported single‐site catalysts for slurry and gas‐phase olefin polymerisation

Early and late transition metal single‐site catalysts revolutionised the polyolefin manufacturing industry and research with their ability to make polymers with uniform microstructural properties. Several of these catalysts are currently used commercially to produce commodity and differentiated‐commodity resins. The key to their rapid success and industrial implementation resided in the fact that they could be used without major modifications in the polymerisation reactors that previously used heterogeneous Ziegler–Natta and Phillips catalysts. Since most of these industrial processes use slurry or gas‐phase reactors, the soluble single‐site catalysts must be supported on adequate carriers that ensure not only high activity, but also the formation of polymer particles with the proper morphology and bulk densities. In this article, we will review several methods used for supporting single‐site early and late transition metal catalysts on a variety of supports. © 2011 Canadian Society for Chemical Engineering     

Preparation of novel MgCl2‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization

In this article, preparation of novel MgCl₂‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization is reported. The factors affecting the particle size (PS) and particle size distribution (PSD) of the prepared support were investigated. In this method, the internal donor added while preparing MgCl₂‐adduct support was supposed to act as a crosslinking agent. Therefore it provided a reasonable way to enhance the morphology and control the PS of the resultant polymer particles. The possible mechanism is discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 945–948, 2006     

Kinetic and morphological study of a magnesium ethoxide‐based Ziegler–Natta catalyst for propylene polymerization

BACKGROUND: Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂‐supported Ziegler–Natta catalyst synthesized from a Mg(OEt)₂ precursor are investigated in comparison with a ball‐milled Ziegler–Natta catalyst. RESULTS: The two types of catalyst show completely different polymerization profiles: mild activation and long‐standing activity with good replication of the catalyst particles for the Mg(OEt)₂‐based catalyst, and rapid activation and deactivation with severe fragmentation of the catalyst particles for the ball‐milled catalyst. The observed differences are discussed in relation to spatial distribution of TiCl₄ on the outermost part and inside of the catalyst particles. CONCLUSION: The Mg(OEt)₂‐based Ziegler–Natta catalyst is believed to show highly stable polymerization activity and good replication because of the uniform titanium distribution all over the catalyst particles. Copyright © 2008 Society of Chemical Industry     

In situ synthesis of polybutene‐1/polypropylene spherical alloys within a reactor with an MgCl2‐supported Ziegler–Natta catalyst

A series of isotactic polybutene‐1/polypropylene (PB/PP) alloys with spherical morphology were prepared by MgCl₂‐supported Ziegler‐Natta catalyst with sequential two‐stage polymerization technology. The first formed PP particles were used as micro‐reactors to initiate the bulk precipitation polymerization of butene‐1 further. The porous PP particles as a hard framework may prevent the adhesion of PB particles during the bulk precipitation polymerization process. At the same time, the bulk precipitation polymerization process allows for maximization of the butene‐1 polymerization rate and simplifies the butene‐1 polymerization process considerably. Finally, spherical PB alloys with a super‐high molecular weight PB component and adjustable PP component were synthesized in situ within the reactor. The structures and properties of the PB/PP alloys were characterized by gel permeation chromatography, ¹³C nuclear magnetic resonance, Fourier transform IR, scanning electron microscopy, differential scanning calorimetry and X‐ray diffraction. The results showed that the MgCl₂‐supported Ziegler‐Natta catalyst showed relatively high stereospecificity and efficiency for both propylene and butene‐1 polymerization. The incorporation of propylene on the PB matrix affects the properties of the final products markedly. The PB/PP alloys are expected to have a broader range of applications as a new family of high performance materials. Copyright © 2012 Society of Chemical Industry     

Blends of ethylene 1‐octene copolymer synthesized by Ziegler–Natta and metallocene catalysts. II. Rheology and morphological behaviors

The rheological and morphological behaviors of commercially available three binary blends of ethylene 1‐octene copolymer (EOC) regarding the melt index (MI), density and comonomer contents, one component made by the Ziegler–Natta and the other by the metallocene catalysts, were investigated to elucidate miscibility and phase behavior. Miscibility of the EOCs blend in a melt state was related to the value of the MI, density, and comonomer content. If the comonomer contents are similar, then the melt viscosity is weight average value, otherwise it is positively or negatively deviated. The microtomed surface prepared by two different cooling processes—one is fast cooling and the other is slow cooling—indicated that all the blends were not homogenous regardless the density, MI, and comonomer content. The Ziegler–Natta catalyzed EOCs exhibited bigger spherulitic diameter and larger ring space than those of the metallocene EOCs prepared by a cooling process. The blends consisting of similar MI showed banded spherulites with different diameter, whereas the blend consisting of different MI and density takes place of explicit phase separation and phase inversion at 1 : 1 blend composition. The melt rheology appeared to influence the mechanical and film properties in the solid state. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1950–1964, 2000     

Morphological study of spherical MgCl2.nEtOH supported TiCl4 Ziegler‐Natta catalyst for polymerization of ethylene

Spherical MgCl₂·nEtOH was prepared by adducting ethanol to MgCl₂ using melt quenching method. Effect of molar ratio of [EtOH]/[MgCl₂] = 2.8–3.05 on the morphology and particle size of the MgCl₂·nEtOH were studied. The best adduct of spherical morphology was obtained when 2.9 mol ethanol to 1 mol MgCl₂ was used. An emulsion of dissolved MgCl₂ in ethanol was prepared in a reactor containing silicon oil. Stirrer speed of the emulsion and its transfer rate to quenching section that work at ?10 to ?40°C are affected by the particle size of the adduct particle. The adducted ethanol was partially removed with controlled heat primary to catalyst preparation (support). Treatment of the support with excess TiCl₄ increased its surface area from 13.1 to 184.4 m²/g. Heterogeneous Ziegler‐Natta catalyst system of MgCl₂ (spherical)/TiCl₄ was prepared using the spherical support. Scanning electron microscopy studies of adduct, support, and catalyst obtained shown spherical particles, however, the polyethylene particles obtained have no regular morphology. The behavior indicates harsh conditions used for catalyst preparation, prepolymerization, and polymerization method used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3829–3834, 2006     

An improved phase‐inversion process for the preparation of silica/poly[styrene‐co‐(acrylic acid)] core–shell microspheres: synthesis and application in the field of polyolefin catalysis

Spherical and well‐dispersed silica/poly[styrene‐co‐(acrylic acid)] (SiO₂/PSA) core–shell particles have been synthesized using an improved phase‐inversion process. The resulting particles were successfully used as supports for polyolefin catalysts in the production of polyethylene with broad molecular weight distribution. Through the vapor phase, instead of the liquid phase in the traditional process, a non‐solvent was introduced into a mixture of micrometer‐sized SiO₂ and PSA solution. The core–shell structure of the resulting SiO₂/PSA microspheres was confirmed using optical microscopy, scanning electron microscopy, Fourier transfer infrared spectrometry, thermogravimetric analysis and measurement of nitrogen adsorption/desorption isotherms. In order to avoid agglomeration of particles and to obtain a good dispersion of the SiO₂/PSA core–shell microspheres, the non‐solvent was added slowly. As the concentration of PSA solution increased, the surface morphology of the core–shell particles became looser and more irregular. However, the surface area and the pore volume remained the same under varying PSA concentrations. The SiO₂/PSA core‐shell microspheres obtained were used as a catalyst carrier system in which the core supported (n‐BuCp)₂ZrCl₂ and the shell supported TiCl₄. Ethylene/1‐hexene copolymerization results indicated that the zirconocene and titanium‐based Ziegler–Natta catalysts were compatible in the hybrid catalyst, showing high activities. The resulting polyethylene had high molecular weight and broad molecular weight distribution. Copyright © 2010 Society of Chemical Industry     

Control of molecular weight distribution in propylene polymerization with Ziegler–Natta/metallocene catalyst mixtures

Propylene polymerization was investigated with a sequential addition of Ziegler–Natta and metallocene catalysts. From the fact that the molecular weights of polypropylene (PP) produced with Ziegler–Natta and with metallocene catalysts differ, it was possible to control the molecular weight distribution (MWD) of PP with a sequential addition of methylaluminoxane and rac-ethylenebis(indenyl)zirconium dichloride followed by triethylaluminum and magnesium dichloride-supported titanium tetrachloride catalyst. The obtained PP exhibited a wide MWD curve with shoulder peak. The position and height of each peak was controlled with the variation of polymerization time for each catalyst as well as the amount of each catalyst. The MWD of PP prepared with sequential addition of catalysts was much wider than that of PP obtained from each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2213–2222, 1998     

Characteristics of diether‐ and phthalate‐based Ziegler‐Natta catalysts for copolymerization of propylene and ethylene and terpolymerization of propylene,ethylene, and 1‐butene

Copolymerization of propylene and ethylene and terpolymerization of propylene, ethylene, and 1‐butene were carried out to compare the characteristics of diether‐ and phthalate‐based Ziegler‐Natta catalysts in a reaction system of pilot scale. The ethylene incorporation with the diether‐based catalyst was higher but the 1‐butene incorporation was lower compared with those of the phthalate‐based catalyst. In the case of copolymers from the diether‐based catalyst, melting behavior, determined through differential scanning calorimetry (DSC), showed a distinct shoulder peak and lots of nuclei were formed during crystallization. The diether‐based catalyst led to polymers having blockier ethylene sequences compared with those of the phthalate‐based catalyst; the highly crystallizable fraction (HIS) containing blockier ethylene sequences was produced with the diether‐based catalyst. These results seem to be the result of regio‐irregular characteristics of the diether‐based catalyst. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 851‐859, 2013